score = eval(input(""))
if score >= 90 and score <=100:
    print("A")
elif score < 90 and score >= 80:
    print("B")
elif score < 80 and score >= 70:
    print("C")
elif score <70 and score >=60:
    print("D")
elif score <60 and score >=0:
    print("E")
else:
    print("Not valid")

